Blanks

"blanks-1.0.0.zip" is a zip archive containing a folder of zipped empty
Macintosh disk image files of various sizes and formats.

First unzip "blanks-1.0.0.zip" to get the folder "blanks".
Then when you need a blank disk image, unzip one of the files
in this folder. For example, unzip "800K.zip"
to get "800K.dsk", an 800K blank disk image, the size of
a floppy disk normally used by a real Macintosh Plus.
It is in "HFS" format (Hierarchical File System),
the standard for a Macintosh Plus.

For information about using disk images in Mini vMac,
see the 'Floppy Drive'
section of the Hardware Reference.
For information about transferring files from your real
computer into and out of disk image files, see
the page about
Disk Images.

The top level of the blanks folder contains 2 other disk images
in the sizes of standard Macintosh floppy disks: 400K and
1440K. A real Macintosh Plus floppy drive could use 400K disks,
but not 1440K, which came later. But Mini vMac doesn't
emulate the real floppy drive, replacing the disk driver
in ROM, and so can use any size disk image, not just 400K and 800K.

The “K” folder contains disk images smaller than 1 megabyte,
in powers of 2 starting at 128K (the smallest that works),
and also multiples 1.25, 1.50, and 1.75 of those powers.

The “M” folder contains disk images larger or equal to
1 megabyte, up to 224M. In general, it may not a good idea to
use the largest sizes, for reasons described below.

The “mfs” folder contains disk images in the
MFS format (Macintosh File System), which preceded HFS.
The original Macintosh 128K and 512K can only use MFS
and not HFS. A Macintosh Plus can use either.

The “dc42” folder contains disk images with
the Disk Copy 4.2 header, and having file
tags and checksums. Mini vMac can support
file tags with the build system option
“-sony-tag 1”,
and can support checksums with the build system option
“-sony-sum 1”.

If you're thinking of using large disk images, keep in mind
that it is not a good idea to create one giant disk image for
all your work. One reason is that the HFS file system is limited to a maximum
of 65535 allocation blocks. So the minimum block size increases for
larger disks, meaning more wasted space. (HFS Plus fixed this
problem, but isn't supported on a Macintosh Plus.) Another reason
it is bad idea is that a Macintosh Plus doesn't have the memory
protection of modern computers, so that a bug in any program
can potentially corrupt mounted disks. It is safer to have separate
disk images for separate purposes. This way Mini vMac gives
the same benefits of memory protection, and more. No matter what program
you run in the emulated machine, nothing can be harmed except
the disk images that are mounted at the time. (Unless there
was a major bug in Mini vMac, of course.)

If you're using Mini vMac on a Macintosh, you might
want to set the file type and creator of your
new disk image file, using
“SetFType”.

It is a good idea to rename the disks
inside the emulated machine, instead of leaving
the default name 'untitled'. Because if two
different mounted disks have the same name,
some programs can become confused. (The name of
the disk which you see in the emulated machine
is completely separate from the name of the
disk image file).

Another issue is that when you
make multiple copies of these blank disk images,
they will have the same creation date. This can
make a difference if you use “Aliases” in System 7.
The Macintosh system software can mistakenly decide
that an already mounted disk is the disk it is looking for,
particularly if it has the same creation date as the correct disk.
If you might encounter this problem, before using one of the blank disk images
you can erase it
(with the “Erase Disk...” command in the Special menu of the Finder)
to make sure it has a unique creation date.

You can also create your own blank disk images of any
size. If you try to mount a file in Mini vMac
which isn't a disk image (preferably all
zeroes) the operating system of the emulated
machine will ask if you want to initialize
it. Choosing 'Initialize' will make
a perfectly good disk image. You can create
zeroed files in the terminal of Mac OS X,
or Linux, with commands such as:

dd if=/dev/zero of=my_image.dsk count=14336

This creates a 7 Megabyte file, named 'my_image.dsk',
in the current directory. 'count'
is the number of 512 byte blocks.

For Microsoft Windows, it is
reported
that the command line utility
MAKEDSK
will make zero-filled files. The same archive also contains
MAKEIMG which generates formatted disk images. However, according
to Disk First Aid and Norton Utilities, the disk images it generates
are not quite in standard HFS format, so it may be safer just to
use MAKEDSK, and let Mac OS in the emulated computer do the formatting.

If you create a zeroed disk image file on a Macintosh,
and wish to set the file type and creator with
SetFType, you should
first mount the zeroed file in Mini vMac to initialize
it, unmount it, and then use SetFType. If you use
SetFType before initializing the file, it won't
know that the file is supposed to be a disk image.